The invention relates to thermally insulating cryogenic ultramicrotome seals.
Cryogenic microtomes and ultramicrotomes generally include an enclosed cryogenic chamber which is cooled by a cryogenic liquid coolant, such as liquid nitrogen, to control the interior of the cryogenic chamber to as low as -196.degree. C. Within the cryogenic chamber are typically located a knife holder and a specimen holder which are moveable relative to one another to produce ultrathin slices of the frozen specimen. Such a known structure can be found in U.S. Pat. No. 3,828,571, the disclosure of which is expressly incorporated herein by reference. These ultrathin samples are necessary for examination of the specimen with, for example, an electron microscope.
Relative movement between the knife and the frozen specimen within the microtome cryogenic chamber can be accomplished by mounting the knife or specimen or both on microtome arms which extend through holes in the cryogenic chamber to the exterior of the chamber where the arms can be manipulated at room temperature. When such microtome arms pass through apertures in the cryogenic chamber, a thermally insulating seal is desirable in order to minimize evaporation of cryogenic liquid contained within the cryogenic chamber and to minimize thermal gradients within the cryogenic chamber which may deleteriously affect the temperature stability of the frozen specimen or knife, or both. At the same time, such a cryogenic seal must not interfere excessively with the precise movement of the microtome arm.